Put bacon fat in a shallow baking dish with garlic, salt, pepper, potatoes, thyme and rosemary. Cover and cook in oven until potatoes are tender, approximately 30 minutes. Strain potatoes and garlic. Set aside. Discard herbs.

Combine yolks and eggs in a bowl and whisk until homogenous. Add cream, salt and pepper.

Place frozen quiche shells on a flat baking pan line with parchment paper. Divide potatoes, a small amount of the reserved garlic, lardons and cheddar cheese among the shells. Pour in the egg mixture and fill to the top. Bake for 30-40 minutes, until eggs are set and caramelized on top.